I have a simple question that is posed as an solution to finding and verifying planets orbiting stars.

Why can we not use an existing tech to solve an age old question of planets in orbit around close stars to our own? I mean the Hubble is great and all but I have yet to see a nice photo of a planet orbiting a distant star.

The rail gun is a very known tech that is growing old on paper more less in practice. So lets build a probe spherical in design that has a magnetically aligned core and several gates that is passes through(In Space) that will increase it's velocity with each gate it passes through.

The rail gun effect could be used to propel a probe to never reached velocities in a matter of < 1sec.

If the probe is only equipped with a very high def camera system, guidance system, ion drive system, transmitters and thrusters it could be placed in orbit of a distant star in a very short time. Then just have it search for planets that are in orbit and set an intercept course to enter into orbit of the most interesting planet for photos.

These probes could be built very cheap and many could be launched in a short time frame.The rail gun type system could be built, powered and attached to the most massive current sat we have in orbit now- the Space Station. This is the only thing up there with the mass to hold such a system in place while the launch occurs.

Its a hard SF story and I think the numbers are in the right ball park area so just to get escape velocity from down here to LEO you would need an accelerator a few hundred Km long and costing in the region of 15-30 $Billion.

For a space based one that gets stuff to up to a significant fraction of c I suspect you would need something in the thousands of Km long. I hope one day we get enough manufacturing capabilities in space to do this kind of science but it wont be for a while yet and also I think you would need antimatter for your fuel to decelerate at the other end and that has not yet been produced in large enough quantity's for this kind of project.

_________________Someone has to tilt at windmills.So that we know what to do when the real giants come!!!!

To start with I did say that it would launch from space not the ground, the launch rings would have to be mounted on something like the ISS to have the mass to hold it in place during operation.

I did get that but a several hundred Km down here linear accelerator just to get to the ISS at 8-11 Km/sec would massively out weigh what we already have up there. The 42Km/sec you would need to just to get out of the solar system would probably need something over a 1000Km long if you were limited to 10Gs(we could probably build more robust probes admittedly but the story i linked to had the calcs for 10Gs) But if you wanted to see a probe arrive while you were still capable of collecting your pension you are talking at least launching at a tenth of c about 30,000Km/Sec and as James pointed out Sir Isaac showed us the universal rules that even a small probe launched like this would significantly skew the ISS's orbit (tho you may get around around this alternately launching in opposite directions)

And from the energy side, ball park back of the envelope figures you would need about 50,000 Kilowatt hours of electricity to accelerate a probe of about a Kg in mass to 1/10th c and the ISS has nowhere near that kind of capacity as as far as I am aware unless they sneaked one of those still classified I think small nuclear rectors up there.

_________________Someone has to tilt at windmills.So that we know what to do when the real giants come!!!!

Jon, JamesG is right. A better use of our money would be to build a “really REALLY big telescope” instead. In particular, I imagine a lunar optical array.

- Deploy thousands of small identical autonomous astronomical mirrors almost randomly on the far side of the moon.

- The independent units operate cooperatively as an adaptive optical system. Being on the far side of the moon shelters the system from earthlight. Being surface based minimizes their long-term energy requirements and greatly simplifies stabilization.

- The mirrors focus on a “receiver” at Lagrangian point two (L2) in the Earth-Luna system.

- The array functions as an optical telescope with a diameter of hundreds of miles. A telescope that size would be able to image exoplanets directly with a resolution high enough to observe surface features.

- Each mirror unit is solar powered. Batteries keep them functioning throughout the lunar night.

- Because they are identical, that many units can be mass-produced comparatively inexpensively.

- Real time data transmission is relayed from L2 to Earth through a satellite in a polar orbit around the moon or in a halo orbit around L2 with a continuous direct line-of-sight to Earth and to the receiver.

- The technology for constructing, deploying and operating the array already exists.

- Using a pay-as-you-go construction schedule means the system becomes functional almost immediately at minimal cost and the resolution improves over time as more and more mirrors are deployed. Identical (or improved) replacements can be deployed as units fail.

- Instead of delivering data from just one planet 40 or 50 years after construction is completed, a lunar optical array would be able to image hundreds of exoplanets immediately and repeatedly at much lower cost.

- The public is much more likely to support a telescope delivering fascinating and tantalizing real-time images from distant worlds which might be very similar to Earth, especially if signs of life were to be discovered.

I agree that some of the big space telescope ideas should be built first. But it would be nice once we had some good candidates to send probes.

I have heard before that the far side of the Moon would be for radio astronomy. But I have never seen any proposals for turning the backside of the moon into a huge Newtonian reflector telescope using the Earth-Moon L2 point any links to papers on this? or is this one you have come up with? IIRC I think the L2 point has also been thought of as part of a lunar space elevator and a propellant depot maybe we could combine all three.

I did worry that the hemisphere of the Moon would make the picture distorted due to relativistic effects. As in caused by the distance to the mirrors between the centre of the far side of the moon under L2 point and those more towards the edge. But having just done the back of envelope calcs I think the pixels on an earth like planet in a similar orbit would only be distorted at about the 15Km level if we could get that high with the rest of the kit so it would still be possible to do a big blue marble type pic rather than a distorted blue dot like I first thought

_________________Someone has to tilt at windmills.So that we know what to do when the real giants come!!!!

I agree, once planets are observed with indisputable signs of life, or at least habitability, we should find a way to send probes. The cheapest and soonest way to go might be nuclear powered ion engines with very big propellant tanks and very long boost phases. We are close to being able to build something like that already. Until then, however, we first have to find suitable candidates for exploration to the satisfaction of the paying public.

Many people have observed that the far side of the moon is an excellent site for enormous radio telescopes or at least an enormous array of more conventional radio telescopes. A stable surface, low gravity and shelter from radio interference from Earth are just a few of the factors favoring construction there. On the other hand, I am not aware of any papers describing a lunar optical array. I just wanted to pass on a thought for your consideration. If anyone knows of any papers on the subject I am sure we will hear about them soon enough.

The Earth-Luna L2 point and orbits around L2 have been used, or proposed for use, for various practical and wholly impractical schemes, most recently as part of a groundbreaking study of aspects of Earth’s magnetosphere. I think there is room enough for everyone.

Fortunately, a large radio telescope array and a large optical array can coexist on the far side of the moon without interfering with each other. One big difference between the two ideas is that the optical array, using existing technology, can be deployed remotely at comparatively low cost and without putting human lives at risk. A huge radio array would probably have to be constructed by crews of hundreds of workers at truly staggering risk and expense, unless some very clever people figure out how to put self-assembling radio telescopes on the lunar surface. I have no doubt somebody is working on it somewhere.

The moon is roughly 2200 miles (~3500 km) in diameter. The width of the array would only be a small fraction of that. The effect of the hemispherical curvature is real but manageable.

While the spectacular images from the Hubble telescope (for example) can be mesmerizing, they can also seem impersonal, literally “distant.” With a lunar optical array, even current (and certainly future) optical hardware and image enhancing software could provide views of tantalizing clarity, making potentially thousands of faraway Earth-like planets seem that much closer. Our fascination with the question of whether anyone like us might call any of those worlds “home” would make further exploration irresistible.

A radio telescope doesn't have to be a single dish. It can be a farm of dishes (or no dishes at all) and still be effective. Like a synthetic aperture radar does not have a traditional dish. In that they would be much easier to emplace and focus than an optical telescope reflector. All of it can be done electronically.

NRAO's LWA1 in New Mexico.

But it would pay to have the individual elements do as many wavelengths as possible since there will be a certain fixed cost in the base, power, and communications required if they were just one band or all of them.

All true, but Jon’s question was about getting “a nice photo of a planet orbiting a distant star.” An optical system will be needed to provide that. The suggestion is that a lunar optical array might be the cheapest fastest way to build an optical telescope big enough to provide that kind of resolution. I’m not sure if “build” is even the right word here. It’s more like a loose formation of autonomous parts of a telescope cooperating to produce an image.

We don’t have to choose one or the other, though. An enormous radio telescope of any configuration and an equally large optical array can both operate on the far side of the moon without interfering with each other.

Many people have observed that the far side of the moon is an excellent site for enormous radio telescopes or at least an enormous array of more conventional radio telescopes. A stable surface, low gravity and shelter from radio interference from Earth are just a few of the factors favoring construction there. On the other hand, I am not aware of any papers describing a lunar optical array. I just wanted to pass on a thought for your consideration. If anyone knows of any papers on the subject I am sure we will hear about them soon enough.

Well I had never heard of the idea before so if your putting out in the public domain here is another idea to possible add to it. The Arecibo which is the only thing I can think of that could be comparable to this even tho its radio and not optical "steers" the scope by moving the antenna. So how about having an adaptive optics mirror and the Gigapixel CCD along with recording control and transmission gear tethered together on opposite sides of a fake halo orbit around L2 with control of the speed of the "orbit" done by pulling in and out masses behind the mirror and the control stuff ice skater style. I think that way you might be able see a bit more of the sky than the narrow band directly where the far side of the Moon is pointing thru its L2 point. If anybody wants to take this idea and run with it I formally put my bit in the public domain.

_________________Someone has to tilt at windmills.So that we know what to do when the real giants come!!!!

The individual mirrors of the array would function much like the heliostats of a large solar power plant, able to redirect a wide angle of incident light to a single focal point. Combine this ability with the orbit of the moon around Earth (and the sun) and all of the zodiac easily becomes available for observation. A longitudinal “stripe” of mirrors would allow most of the rest of the celestial sphere to be observed as well.

The Arecibo reflector of course is stationary, so the receiving antenna must move instead. “Receiver” was not quite the right word for the L2 component when I first described the idea for a lunar optical telescope a few posts back, but I’m not sure what else to call it. That’s why I put it in quotation marks. Even the word “array” is not a perfect fit because the mirrors would be fairly randomly dispersed over the target area rather than laid out in a tidy grid. Your description of the system as a huge Newtonian telescope is close enough for me.

By the time such a thing might actually be deployed we’ll probably be talking about terapixel CCDs!

Ah it maybe I was overcomplicating things I was thinking that with a fixed point in the system, the L2 one you could only have one focused parabola that moved as the Moon moved but the solar power plant heliostats analogy makes me think I may have had a failure of imagination on how the light would bounce about unless of course heliostats reflect the light to a single point as they do but would produce a distorted overlayed image of the sun at several different angles at the focal point. But I am not 100% sure either way as its a few decades since I did my o'level physics(And something like this would be a lot of extra credit ) and agree the heliostats idea would be easier to implement if does create one in focus image.

And yes at the snails pace we have been going since the last trip to the Moon an iPhone N.0 might have terrapixel capabilities before the far side of the Moon does.

_________________Someone has to tilt at windmills.So that we know what to do when the real giants come!!!!

I picture the idea more like this, but more spread out and of course without the objective mirrors on each one.

Think of it like being a huge DLP projector, where each primary mirror can be precisely adjusted both in angle and "concavity" for focus upon the objective lens or lenses that are out at L2, hopefully doing it's best to hold very still (not easy in the Moon's lumpy gravity).

Much more technically challenging that a simple radio telescope, or a whole bunch of little telescopes, but has the potential to scale up to have an enormous angular resolution and light-gathering capability.